It has been well known to provide plastic wear members for railway vehicles. For example, U.S. Pat. Nos. 4,188,888; 4,237,792 and 4,289,077 show wear members in the form of liners for center bearings of trucks. Wear members of plastic have also been widely used at the sliding surfaces of coupler members, as disclosed in U.S. Pat. Nos. 4,238,039; 4,249,665; 4,261,472, and 4,264,015. Plastic wear members have further been used for pedestals of a railway truck, as disclosed in U.S. Pat. Nos. 4,237,793 and 4,239,007; and for brake rods, as disclosed in U.S. Pat. Nos. 4,079,818 and 4,452,345.
Heretofore, it has been known to provide a wear plate of plastic material for a sliding sill support, as disclosed in U.S. Pat. No. 4,348,964. This wear plate is made of a resilient material having a low coefficient of friction and is formed to fit on a specific sized support member. Accordingly, for different installations another size wear plate member must be used.
It has also been known to provide custom-made wear plates which include plastic pads bonded to steel base plates wherein the base plate is mounted to a sliding sill support by welding the base plate in place. Since it is custom made, it requires the stocking of a number of different wear plates in order to service various applications. Further, the plastic body in some versions is of such a length that during the bonding operation the metal base plate may become warped or have a "banana effect". Additionally, where the plastic pad is of a rather long length, it tends to delaminate in extremely cold or hot weather because the coefficient of expansion of the plastic material is much higher than that of the metal base plate. Plastic usually has a coefficient of expansion of about ten times greater than steel.
Heretofore, where various sizes of wear plates were needed to handle all installations, multiple molds were required for molding the plastic pads as the wear plates were customized. Further, where long wear plates were required and only a weld allowed at each end, the wear plate would be subjected to the "oil can" or buckling effect when undergoing severe temperature shifts because of the differential in the coefficient of expansion of the plastic material and the metal base. This "oil can" effect will eventually crack the welds and the wear plates will fall out.
It was also known to use large sheets of plastic for certain installations that measured four feet by eight or ten feet and which had to be secured in place by mechanical fasteners which necessitated providing slotted holes in the plastic to allow for expansion and contraction.
These wear members have been developed following the availability of suitable plastic resins and particularly certain polyethylenes, such as a linear high-density polyethylene which is usually referred to as an ultra-high molecular weight polyethylene. As disclosed in some of the above patents, these plastic materials have been bonded to metal supporting members which are then mounted on supporting parts of a railway vehicle, or used in sheets and secured in place.